1. Field of the Invention
The present invention relates to a method of improving the state of the surface of a roll, in particular of a rolling mill roll or continuous annealing roll, by means of a concentrated corpuscular beam, such as a laser beam or an electron beam.
2. Description of the Prior Art
It is known that the state of the surface of rolling mill rolls, in particular their roughness, determines the surface quality of the metal sheets to a very large extent. In particular, during reduction rolling, it is possible by means of suitable rolls to provide the sheets with a degree of roughness which enables the adhesion of the turns during coil annealing to be avoided. Moreover, the roughness of sheets which have been subject to temper rolling after annealing substantially affects their ability to undergo a shaping operation and to receive a coating.
Attempts have already been made to replace the random roughness of the rolls, such as results from shot blasting for example, with a deterministic type of roughness whose distribution could be mastered more easily.
In particular it has been proposed, in Belgian Pat. No. 880 996, to form microperforations on the surface of rolling mill rolls by means of a laser beam. According to this known method a continuous laser beam is rendered intermittent; then it is focused on the surface of the roll to be treated, where it locally destroys by fusion the material forming the roll. The entire surface is treated by rotating the roll about its axis and by displacing the concentrated beam, which thus scans the entire surface, parallel to this axis.
During these movements the impact zone of the beam on the roll surface describes a helical course along which the desired microperforations are distributed.
When it is desired to operate without rendering the beam intermittent, the roughness obtained has a high degree of anisotropy since it is constituted by a sort of "thread" which, during rolling, is transformed into lines in the surface of the sheet in the direction of rolling.
It is, however, suitable to reduce, or if possible to eliminate, this anisotropy since it impairs the appearance of the rolled sheets and harms the isotropy of their working properties. This latter effect is particularly undesirable in the case of press forming, for example deep drawing.